Recovery of sulfur from native sulfur-bearing ores



Jan. 9, 1951 P. J. MCGAULEY ETAL RECOVERY 0F SULFUR FRQM NATIVE SULFUR-BEARING ORES Filed Dec. 1s, 1948 in the interstices of the gangue. invention, while taking advantage Patented Jan. 9, 17951 T orrlcs RECOVERY F SULFUR FBGM NATIVE SULFUR-BEARING ORES Patrick J. McGauley, Glen Cove, Roberts and Samuel Strelzoil,

and Edward S'. New York, N. Y.,

assignors to Chemical Construction Corporation, New York, N. Y.

Ware

. a' corporation of Dela- Appueatmn December 1s, isla, sei-n1 No. 66.122 12 claim.. (cl. 241-17) This invention relates to a method of recovering sulfur from native sulfur-bearing ores; that is, from ores which contain free elemental sulfur. The principal object of the invention is to provide a process which will extract substantially all of the sulfur from the ore, with recoveries from a single cycle on the order of 90% or better, and which will produce 'a commercially l pure sulfur.

There are'many deposits of native sulfur-bearing Iores throughout the world which are sumciently rich in sulfur to warrant commercial development if a satisfactory recovery and purification process were available. Typical of these are deposits in Colombia, in ,Egypt, and in the island of Milos, all of which have av free sulfur content within the range of about 20-35% or better. Attempts have previously been-made to separate this sulfur from ores of this type by melting and agglomeration processes, in which the ore is heated to a temperature above the melting point of sulfur 113-120 C.) to cause the sulfur droplets to run together and separat,l from the ore. However these processes are not commercially usable with some ores, notably those containing the sulfur in very finely distributed form throughout the ore, as in Egyptian ores. Moreover, the sulfur recoveries -obtainable by these processes seldom exceed 50-75%, and even with the most favorable ores, a recovery of about 80% of the sulfur is the best that can be oby agglomeration process is the fact that a certain' proportion of the molten sulfur is inevitably held The pr` sent of the principle of agglomeration separation to the extent that yit can be used with the particular ore under treatment, provides an improved method of separating the sulfur phase from the gangue material. This is done by the use of froth flotation.

It has many times been proposed to separate sulfur from sulfur-bearing ore by grinding the ore and subjecting it to a. froth flotation process. Attempts to carry out these proposals on a commereial scale, however, have always encountered difficulties caused by the presence of inely dlvided sulfur in the ground ore. During the grinding step a substantial proportion of the free sulfur in the ore is always disintegrated into ilne sulfur particles which, during the flotation process, attach themselves to the bubbles of froth. By coating the surfaces of the bubbles, these nes stabilize the froth and reduce its ability to re- 2 y v lease particles of gangue, thus impairing the selectivity of the flotation and lowering the grade of the concentrate produced. j

The present invention overcomes all of the above diillculties and produces a pure -sulfur with a high percentage of recovery by rst heating and agitating an aqueous slurry of the ground sulfur-bearing ore for a short time at a temperature above the melting point of sulfur Vto cause the fine sulfur particles to coalesce into larger aggregates containing less exposed sirface. The slurryis then cooled to a temperature below the melting point of sulfur and subjected to froth flotation, preferably at relatively high temperatures of about 50-100 C., followed by remelting and filtering the sulfur obtained in the flotation concentrate. v

If the ore being treated is one from which a substantial proportion of the sulfur separates during the heating andagitating step, the sulfur so obtained may be drawn off as liquid sulfur during the heating step, or the agglomerated sulfur may be screened from a slurry after it has been cooled, either prior to or after flotation. In either event. the sulfur so obtained is is separated out in this manner during the practice of the preferred embodiments of our inven-` tion.

, Ihe invention will be further described with' reference to the accompanying drawings, in which the single figure is a flow diagram in'which the various steps of a complete process are illustrated.

In carrying out the process of our invention,Y

a native sulfur-bearing ore .such as any of those referred to above may Se crushed and, if desired. may be given a preliminary beneiiciation by any suitable process. It is then ground and screened with return of oversize to the grinding process, preferably to a maximum particle size within the range of 10-40 mesh, although liner grindingup to through mesh or smaller may be used in some cases if this should prove to be desirable.

It is, however, an importantadvantage of the invention that in most cases fine grinding need not be resorted to.

`After thew ore has been ground, which always causes some 50% or more of its sulfur content to preferably melted.' and filtered along with the sulfur from theflotag be disintegrated into nes having a particle size of on the order of 1-5 microns, the ground material is slurried in water. In most cases sunlcient water is used to form a slurry of about 15-50% solids content; however. the concentration of the slurry is not critical and is usually kept as high as possible, consistent with the ability of a pump to force it into the coil or other heating vessel. When flotation middlings from the process are recycled to the slurrying step, their water content is of course considered in calculating the proper amount of water to be added to produce a slurry of the desired density. Where hot water is available from the process, as is illustrated on the attached flow sheet, it may be used to form the slurry, thus reducing the amount of high-pressure steam consumed in the heating coil. Any suitable apparatus may be used for preparing the slurry, a tank l provided with an agitator 2 being diagrammatically illustrated on the drawing.

The slurry prepared in the tank I is forced through pipe 3 into a heating and agitating coil 4, preferably by means of a pump such as that shown at 5I. Steam at 2li-50|` pounds per square inch gauge pressure. or higher, is introduced through pipe 6 and is mixed directly with the slurry in the pipe coil, while the turbulence cre- `ated by its introduction and by ,passage of the mixture through the coil lresults in vigorous agitation. When the temperature of the slurry in the coil is above the melting point of sulfur, the

sulfur fines produced in the grinding step are quickly agglomerated by adhesion to each other.`

We have found that under the conditions stated the agglomeration of the sulfur ilnes takes Place very rapidly, a time of about -60 seconds usufeature of our process can be carried out both,

continuously and at an extremely high production rate, as compared with prior sulfur recovery procedures where the heating was relied upon to separate the entire yield oi sulfur from the ore.

After the slurry hasl been heated for the required length oi time in the coil l it 'should be cooled rapidly to a temperature below the melting point of sulfur, and preferably below 100 C. so that no boiling will occur when the pressure is released. This is preferably accomplished by iniecting cold water into the slurry by means of the pipe 5 as it passed through line 36 and pressurereducing valve 1. The conditioned slurry then discharges through pipe 8 into a storage tank 9. In this tank it may be diluted and adjusted to flotation density by the addition of water through the line I0. The normal pulp densities usually employed in froth flotation (i. e. about 25% solids) are used in practicing our invention.

Theparticles of agglomerated sulfur are separated from the gangue by a froth notation process, with or without a preliminary screening. Conditioned slurry from the storage tank 9 is withdrawn through line Il and may be screened, if desired, on a rotary screen I2 to remove oversized lumps of sulfur; this screen preferably has a mesh size of about the same as that used for screening the ground raw ore. Lumps of sulfur collected on the screen are introduced into the melter and sulfur illter that will be subsequently described. It should be emphasized, however, that the screening step is optional and may be eliminated from the process, the pulp from the storage tank 9 being passed directly to the notation process.

Flotation of the conditioned ore pulp is preferably carrled out in two or more notation cells which may be, for example, of the Fagergren type. These notation machines consist essentially of a flotation chamber containing a stator composed of a ring of spaced vertical cylindrical bars, within which is mounted a cylindrical rotating cage having vertical sides that are also composed of spaced cylindrical bars. The top of the cage is attached to a hollow rotating shaft, through which air is drawn by the vortex action. The relative motion of the rotor bars past the stator bars eectively disseminates the occluded air into fine bubbles and evenly distributes them throughout the mass of the slurry. These ilne bubbles collect the non-wetable sulfur particles in the pulp and raise them to the surface. Pine oil in amounts of (LOI-0.03 pound per ton oi.' ore or sodium dicresyldithiophosphate, or both, may be used as frothing or collecting agents in the flotation process. The flotation is preferably carried out under acid conditions, the pH being maintained at about 3.0. As is noted above, greatly improved results are obtained when the notation is carried out at 40-100" C., and, therefore. the pulp is passed through the notation machine at a temperature within this range and preferably at 60-90" C. It is a peculiar advantage of the invention that the heat used to cause agglomeration of the fine sulfur particles in the coll 4 may also be used to improve the eillciency of the flotation.

The rst flotation cell I 4, or group of cells, is operated as a rougher, the tailings from this group being discarded. The concentrate is passed through' a trough or other conveying line I5 to one or more cleaner flotation cells I6 where it is again floated at about the same temperature to produce a semi-refined sulfur concentrate of about Sil-% purity, depending on the particular ore. The middlings, or tailings from the second flotation, are passed through line i1 to a thickener I8, from which the thickened pulp is returned through line I9 to mix with additional conditioned slurry in the pipe 2li for return to the rougher flotation I4. Alternatively the thickened middlings may be returned to the slurry tank I. Overflow from the thickener I8 passes through lines 2i and 22 to the hot water storage tank 23. The tailings from the rougher flotation cells Il are also thickened in a thickener 24, from which the overflow water passes through line 25 to the storage tank 23. The pulp Withdrawn from the bottom of this thickener through line 28 is discarded.

The concentrate from the cleaned flotation cells I6 is passed through trough 21 to thickener 28, from which the overflow water is also passed to the het water storage tank 23 through line 29. The thickened pulp leaving through line 30 is dewatered on a filter 3| and is then heated, as by steam coils 32, in a melter 33, to which screenings from the screen l2 may also be added. The molten sulfur product leaving the melter 33 is passed through line 34 to a steam-heated sulfur filter 35, from which a ltrate consisting of commercially pure sulfur is recovered. For this purpose a leaf-type filter may be employed in which a plurality of filter leaves are immersed in the sulfur to be filtered, the purified sulfur being withdrawn from the interior of the leaves and the iilter cake collecting on the outer surfaces thereof.

The foregoing is '.v description of the best meth-` od at present known to us for practicing the invention, but it should be understoodthat other types of equipment may be substituted for those illustrated ldiagrammatically in the drawing.

' accumulates in the vessel. As a further alternative the ore slurry may be heated indirectly, as by a steam jacket surrounding the c'oil 4, instead of by the direct injection of steam. It will also be understood that'the ore slurry, after being heated for about 0.25-5 minutes in the pipe coil, autoclave or other pressure vessel, can be cooled to a temperature below the melting point of sulfur by indirect cooling, as by passage through a pipe surrounded by a jacket of cooling water, if desired. Other forms of apparatus for carrying out the steps of the invention will readily suggest themselves to those skilled in the art. y

Our experiments have shown, however, that for most native sulfur-bearing ores a pipe coil lof the type illustrated in the drawings is greatly preferable, and therefore we will describe such a coil in detail. In obtaining the results shown in the following specific examples we employed a set of pipes of 1A inch internal diameter, covered with suitable insulation and joined at their ends by U-turns. At one end of the coil, valved pipes were inserted in the U-turns so that steam could be injected into each coil separately, while similar valved by-pass lines connected the U-turns at the opposite end of the coil to a common header.

By opening and closing the valves in these bypass lines the time of sojourn of the slurry in the heating coils could be adjusted. A total of seven 10-foot lengths of pipe were used in this coil arrangement with by-pass adjustments such that from a single length to the ventire coil system could be used as desired.

The invention will be further illustrated by the following specific examples of results that have been obtained with particular ores and under particular operating conditions. It should be understood, however, that although these examples may describe in detail some 'of the preferred embodiments of the invention, they are' given primarily for purposes of illustration and the invention in its broader aspects is not limited thereto.

Example 1 vjected, thereby heating the slurry to about 130 C. 'I'he residence time of the slurry in the coil A portion of the conditioned slurry containing 414 grams oi' solids was screened on a 28 mesh wire cloth, which retained 6 grams of sulfur having a purity of about 98%. The remaining slurry, containing 408 grams of solids, was subjected to notation at 85 C. in a Fagergren batch flotation machine at a pulp density of about 20% solids using pine oil and sodium dicresyldithiophosphate. 'Ithe notation time required was less than 11/2 minutes.

The products obtained were:

(a) 158 grams dry weight of concentrate containing 122.4 grams of sulfur.

(b) 250 grams dry weight oi' tailings containing 7.2 grams of sulfur.

The tailings, representing a loss of 5.2% of the sulfur in the ore, were discarded. I'he concen- Itrate was repulped with water at 65 C. to about the same flotation density and again separated by froth notation into:

(c) 109 grams of concentrate (dry weight).

taining`105 grams of sulfur.

(d) 49 grams( of middlings (dry weight) containing 17.4 grams of sulfur.

(e) The middlings were reiloated in admixture with a second portion of the conditioned and screened ore whereby 16.5 grams of its sulfur sure ltered through a glass iilter cloth. The ltrate was 124 grams of sulfur having a purity of 99.5%. The lter cake contained approximately 50% of sulfur, most of which could be recovered -by mixing it with raw ground ore in the original slurry tank.

The net result of this treatment was, therefore, that 'about 92%' of the sulfur in the ore sample was. recovered as-a commercial product of 99.5% purity; about 3% of the sulfur was recirculated through the process,and about 5% was lost in the gangue.

Example 2 The procedure of Example 1 was repeated with the addition of varying quantities of ground raw ore to the flotation feed in order to demonstrate the adverse effect of the sulfur slimes so was `approximately 30 seconds, after which the` slurry was immediately cooled to C. by admixture with cold Water.

introduced.

To another portion of the conditioned (steamtreated) slurry of Example 1 there was added grams of the raw ore as it existed just prior to the rst step; i. e., after grinding and screening throughy a 28 mesh screen. The resulting pulp, without screening, was diluted with hot water to 20% solids and subjected to rougher and cleaner flotations at 85 C. and 65 C., with return of the middlings to the rougher flotation and iiltration of the concentrates, exactly as described in Example 1. By this procedure there was obtained:

(a) .144 grams of commercial sulfur of 99.5% purity, equal to 82.8% of the sulfur in the ore.

(b) 325 grams of tailings, containing 6.3% of the sulfur in the ore, which were discarded.

(c) 38 grams of nlter cake, containing 10.9% oi' the sulfur in the ore.

A third test was made in which only raw ore was used. 327 grams of unconditioned ore, ground and screened through the 28 mesh screen, was suspended in hot water to solids and subjected to the treatments described above with the following results:

(d) 42 grams of 99.5% pure sulfur, equal to 36.6% of the sulfur in the ore, were recovered as iiltrate.

(e) 153 grams of'tailings containing 6.8% of the sulfur in the ore were discarded.

(f) 132 grams of filter cake, containing 57.6% of the sulfur in the ore.

Example 3 Another sample of the Colombian ore of Example 1 was ground and screened through a 28 mesh screen, slurried in water and treated with steam in the coil as described in that example, but the residence time in the coil was increased to 3 minutes. sulting from the longer heat treatment was that a vlarger proportion of the sulfur separated out during the screening prior to flotation.

The conditioned pulp was separated into several portions which were subjected to the flotation treatments described in Example 1 at different temperatures; the same pulp density being used throughout.

No. 1.-The ore was floated at .85 C. and the screenings and flotation concentrates were melted and filtered. The recoveries were:

(a) Approximately 156 grams of commercial sulfur, equal to 92.2% of the sulfur in the ore, were obtained as filtrate.

(b) 277 grams of tailings containing 4.7% of the sulfur in the ore were discarded.

(c) ll grams of filter cake containing 3.1% of the sulfur in the ore required recycling.

No. 2.-Flotation at 60 C. 'I'he results were:

(a) 137 grams of filtrate, equal to 88.5% of the sulfur in the ore.

(b) 309 grams of tailings containing 8.7% of the sulfur in the ore. -4

(c) 9 grains of lter cake containing 2.8% of the sulfur in the ore.

No. 3,-Fiotation at 40 C. The results were:

(a) 145 grams of nitrate, equal to 88% of the sulfur in the ore.

(b) 290 grams of tailings containing 6.6% of the sulfur in the ore.

(c) 18 grams of filter cake containing 5.4% oi' the sulfur in the ore.

No. 4.-Flotation at C. The results were:

(a) 128 grams of filtrate, equal to 74% of the sulfur in the ore.

(b) 298 grams of tailings containing 15.3% of the sulfur in the ore.

(c) 38 grams of lter cake containing 10.7% of the sulfur in the ore.

These tests show the importance of conducting the flotation at temperatures of Iat least 40 C., and preferably at 60-90 C. When the temperature is below about 40 C. the percentage of sulfur lost in the tailings increases rapidly and the grade of the flotation concentrate is low- The only noticeable diierence re- 8 ered. as shown by the increased weight of the nlter cake.

Example 4 A sample of a native sulfur-containing ore from the island of Milos,l Greece, was treated by the procedure described in Example 1. In this ore the gangue was a rather pure siliceous volcanic ash. The products obtained were as fol- ]OWS I (a) The filtrate'was 67 grams of commercially pure sulfur; equal to 97.5% of the sulfur in the ore sample.

(b) 213 grams of tailings were discarded containing 0.9% of the sulfur in the ore.

(c) 2 grams of lter cake, containing 1.8% of the sulfur in the ore, required recycling.

Example 5 A sample of sulfur ore from the Gemsa peninsula of Egypt was treated by the process of Example 1. In this ore the sulfur was disseminated in the form of vfery ne particles throughout a gangue consisting of amixture of silica and imil;.uiil'leedgypsum. 'Ihe following products were ob- (a)' 148 grams oi' sulfur of commercial purity,

- equal to 89.4% of the sulfur in the ore.

(b) 272 grams of tailings containing 6.9% of the sulfur in the ore.

(c) 12 grams of lter cake containing 3.7% of the sulfur in the ore.

what we claim is: Y

1. A method of recovering sulfur from n native r tion at normal flotation pulp density, removing as ilotation concentrate a semi-puried sulfur, and melting and filtering said semi-purified sulfur to produce a sulfur ofl 99100% purity.

2. A method according to claim 1 in which the ore is ground and screened to a maximum particle size of 10-40 mesh and suspended in water to a slurry of about 20-50% solids.

3. A method according to claim 1 in which the slurry is heated by direct injection of steam to 1Z0-135 C.

4. A method according to claim 1 in which the slurry, after cooling but before otation, is screened to remove lumps of agglomerated sulfur and the lumps so removed are melted and filtered along with the semi-puried sulfur from the iiotation concentrate.

5. A method according to claim 1 in which the flotation is carried out at a temperature within the range of 40-100 C.

6. A method of recovering sulfur from a native sulfur-bearing ore which consists of the steps of grinding and screening said ore to a maximum particle size of 10-40 mesh, during which a portion of its free sulfur is disintegrated into fines, suspending the ground ore in water, heating the resulting slurry with agitation to a temperature of 135 C. and during a time of about 0.25-5

minutes to cause said nes to coalesce, cooling the slurry to a temperature below the melting point of sulfur and subjecting it to a froth notation at normal flotation pulp density, removing as flota- 'tion concentrate a semi-purified sulfur, and meltlflotation concentrate.

8. A method according to claim 6 in which the flotation is carried out at a temperature within the range of about 60-90 C.

9. A method of recovering sulfur from a native sulfur-bearing ore which consists of the steps of grinding Said ore, during which a portion of its free sulfur is distintegrated into fines, suspending the ground ore in water, heating and agitating the resulting slurry to a temperature above the melting point of sulfur by forcing it during about 0.25-5 minutes through a narrow passage While injecting steam therein and thereby causing said nes to coalesce, injecting cold water into `said slurry and thereby cooling it below the melting point of sulfur, diluting'theslurry to normal flotation pulp density and subjecting it to froth flotation and removing as flotation concentrate a semi-purified sulfur, and melting and filtering said semi-purified sulfur to produce a sulfur of 99-100% purity! 10. A method according to claim 9 in which the steam is injected at a pressure of 20-50 lbs. per square. inch gauge.

11. A method according to claim 9 in which the slurry, after cooling but before notation, is screened to remove lumps of agglomerated sulfur and the lumps so removed are melted and filtered along with the semi-purified sulfur from the flotation concentrate. f y

12. A method of recovering sulfur from a native sulfur-bearing ore which consists of grinding said ore, during which a portion of its free sulfur is disintegrated into fines, suspending the ground ore in water along with filter cake from the process to form a slurry of about 20-50% solids, heating said slurry for a period of from 0.25 to 5 minutes with agitation to a temperature above the melting point of sulfur to cause said fines to coalesce, cooling the slurry to a temperature within the range of about 60-90 C.'and subjecting it at normal flotation pulp density to a rougher flotation at this temperature and discarding the tailings therefrom, subjecting the concentrate from said rougher flotation to a cleaner flotation at about the same temperature and dewa-tering, melting and filtering the cleaner concentrate therefrom to produce a sulfur of 99-l00% purity, and returning lter cake from l said ltering step to said slurrying step for reworking.

PATRICK J. MCGAULEY. EDWARD S. ROBERTS. SAMUEL STRELZOFF.

REFERENCES CITED y The following references are of record in the Name Date Nutter et al Jan. 1, 1929 Number 

1. A METHOD OF RECOVERING SULFUR FROM A NATIVE SULFUR-BEARING ORE WHICH CONSISTS OF THE STEPS OF GRINDING SAID ORE, DURING WHICH A PORTION OF ITS FREE SULFUR IS DISINTEGRATED INTO FINES, SUSPENDING THE GROUND ORE IN WATER, HEATING THE RESULTING SLURRY WITH AGITATION TO A TEMPEATURE ABOVE THE MELTING POINT OF SULFUR FOR A PERIOD OF FROM 0.25 TO 5 MINUTES OF CAUSE SAID FINES TO COALESCE, COOLING THE SLURRY TO A TEMPERAUTRE BELOW THE MELTING POINT OF SULFUR AND SUBJECTING IT TO A FROTH FLOTATION AT NORMAL FLOTATION PULP DENSITY, REMOVING AS FLOTATION CONCENTRATE A SEMI-PURIFIED SULFUR, AND MELTING AND FILTERING SAID SEMI-PURIFED SULFUR TO PRODUCE A SULFUR OF 99-100% PURITY. 